1. Field of Invention
The present invention is related to on-demand information systems that broadcast program content to mobile receivers for capture, storage, and subsequent playback of the stored content to a user.
2. Related Art
Cellular wireless (e.g., radio) communication systems that provide telephone links between a public switched telephone network (PSTN) and mobile transceivers (e.g., cellular telephone handsets or xe2x80x9cmobilesxe2x80x9d) are well-known. FIG. 1 illustrates a typical cellular tiling pattern of seven cells 1-7. A base station is typically positioned in each cell. Both the base stations and the mobiles operate using transmit power levels that are low enough so that interference does not occur in similarly numbered cells in adjacent patterns. For example, base station 10 that operates in cell 1 of tiling pattern 11 does not interfere with base station 12 that operates in cell 1 of an adjacent tiling pattern 13. Thus frequencies can be reused over a wide geographic area.
In the United States, cellular wireless communications systems are assigned specific operating frequency spectra. In the United States analog cellular system, for example, uplink communication (mobile to base station) occurs in 30 kilohertz (kHz) channels in the frequency spectrum from 824 megahertz (MHz) to 849 MHz. Downlink communication (base station to mobile) occurs in other 30 kHz channels in the frequency spectrum from 869 MHz to 894 MHz. In this frequency channel assignment scheme, 45 MHz separates the uplink and downlink channels, and therefore 833 pairs of uplink-downlink channel pairs are created. In the United States, the uplink-downlink pairs are allocated among two commercial service providers for public policy reasons. The 25 MHz uplink and downlink spectra are therefore divided in half, with each service provider using 416 uplink-downlink channel pairs. The channel pairs are further divided among the cells in each tile pattern.
The U.S. digital cellular system is backwards compatible with the analog frequency spectrum and supports three simultaneous radio links within the bandwidth used for one analog radio link. Spread spectrum cellular systems (e.g., code division multiple access (CDMA)) also reuse coded channels in a similar way. Thus the term xe2x80x9cchannelxe2x80x9d as used in this description includes an analog voice channel in an analog cellular system, a time slot of a digital voice channel in a time division multiple access (TDMA) digital cellular system, and a coded channel in a code division multiple access (CDMA) digital cellular system.
Channels in each cell are designated as setup, paging, or voice traffic channels. For instance, in a geographic coverage area, each commercial cellular service provider is allocated 21 setup (uplink) and 21 paging (downlink) channels (3 per cell in a k=7 tiling pattern), and therefore 395 voice traffic channels remain for each service provider to use (approximately 56 unique voice channel uplink-downlink pairs per cell in the k=7 pattern). The number of voice channels in use varies during the day. For example, during peak voice traffic time (e.g., 5:00 p.m. (1700)), most of the voice channels in individual cells are in use. During non-peak times (e.g., 3:00 a.m. (0300)), however, most of the voice channels are unused. Thus a large portion of the cellular spectrum is unused during the day.
Audio/video-on-demand systems broadcast content (e.g., information and entertainment programs such as news, music, financial information, traffic reports) to users (system subscribers). The broadcast content is selectively received (captured) by and stored in mobile receivers (local storage) for subsequent output (playback) to the human user (see e.g., U.S. Pat. Nos. 5,406,626, 5,524,051, and 5,590,195, each incorporated herein by reference). Existing audio/video-on-demand systems broadcast content on portions of the radio frequency spectrum such as sidebands of commercial FM radio station frequencies. But, additional bandwidth is required as the amount of content that is offered to audio/video-on-demand subscribers increases.
In accordance with the invention, unused channels in a cellular wireless communications system frequency spectrum are used for broadcast of content to mobile audio/video-on-demand receivers. The number of channels that are used to broadcast content to the receivers is varied as demand for voice traffic channel changes. The quantity of unused channels is identified, and an amount of program content that is stored in a database is accessed based on the quantity of unused channels. The accessed program content is formatted for broadcast on at least a portion of the unused channels. The formatted content is then transferred to the cellular wireless communications system for broadcast to the mobile receivers.
In some embodiments a content transmission schedule is broadcast on one of the unused channels. The transmission schedule includes the program content identifier for the programs being broadcast and the channel on which the program is broadcast. In some embodiments the transmission schedule includes the time at which particular programs will be broadcast.